1. Field of the Invention
The present invention relates to a damper mechanism. More specifically, the present invention relates more particularly to a damper mechanism for damping torsional vibrations in a power transmission system.
2. Background Information
Clutch disk assemblies used in vehicles function as a clutch for engaging and disengaging a flywheel to facilitate the transfer of torque from an engine. Clutch disk assemblies also function as a damper mechanism for absorbing and damping torsional vibrations from the flywheel. In general, vehicle vibrations include idling-related noises such as rattling sounds, traveling-related noises such as rattling associated with acceleration and deceleration and muffled noises, and tip-in/tip-out or low frequency vibrations. The damper function of the clutch disk assembly is provided ideally to eliminate these noises and vibrations.
Idling-related noises are rattling noises that emit from the transmission when the gearshift is put into neutral and the clutch pedal is released. For example, while waiting at a traffic light a driver might shift the gear into neutral, causing the transmission to rattle. When the engine is running at a speed in the vicinity of idling speed, the engine torque is relatively low and the torque change at the time of each power stroke explosion is relatively large. Under these conditions, the teeth of the transmission input gear and counter gear undergo a phenomenon of striking against one another.
Tip-in and tip-out or low frequency vibrations refer to large-scale lengthwise shaking of the vehicle that occurs when the accelerator pedal is depressed or released suddenly. If the rigidity of the drive transmission system is low, the torque transmitted to the tires is transmitted back from the tires as torque and a resulting lurching reaction causes excessive torque to be generated at the tires. As a result, longitudinal vibrations occur that shake the vehicle excessively back and forth.
In the case of idling noises the problem lies in the zero torque region of the torsion characteristic of the clutch disk assembly. The problem is alleviated if the torsional rigidity is low. Conversely, it is necessary for the torsion characteristic of the clutch disk assembly to be as rigid as possible to suppress the longitudinal vibrations caused by tip-in and tip-out.
In order to solve this problem, a clutch disk assembly has been proposed which has a two-stage characteristic obtained by using two types of springs. The first stage or low twisting angle region of the torsion characteristic has a relatively low torsional rigidity and low hysteresis torque, and provides a noise preventing effect during idling. Meanwhile, the second stage or high twisting angle region of the torsion characteristic has a relatively high torsional rigidity and high hysteresis torque. Thus, the second stage is sufficiently capable of damping the longitudinal vibrations of tip-in and tip-out.
A damper mechanism that efficiently absorbs small torsional vibrations is also known. The damper mechanism is configured to have a low hysteresis torque in the second stage of the torsion characteristic and does not allow a large friction mechanism of the second stage to operate when small vibrations are inputted due to such factors as combustion fluctuations in the engine. A damper mechanism with a rotational gap has been provided. The damper mechanism does not allow the large friction mechanism of the second stage to operate within a prescribed angular range in the second stage of the torsion characteristic. The damper mechanism is arranged, for example, such that a rotational gap is secured between two members and the large friction mechanism of the second stage is not allowed to operate within the scope of the gap. However, since the frictional resistance is small within the gap, variations in the rotational speed of the engine cause the two members to strike constantly against each other and thus be subjected to physical shock. Consequently, over a long period of use, the two members wear causing the gap to become larger than the original gap setting. When the gap in which the large friction mechanism of the second stage is not allowed to operate becomes larger, the ability of the mechanism to absorb noise and vibrations declines.
In view of the above, there exists a need for a damper mechanism that overcomes the above-mentioned problems in the prior art. This invention addresses this need in the prior art as well as other needs, which will become apparent to those skilled in the art from this disclosure.